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ruby-rdf / rdf-rdfxml

Ruby RDF/XML reader/writer for RDF.rb.
http://rubygems.org/gems/rdf-rdfxml
The Unlicense
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Undefined xpath for nil:NilClass (0.3.5 in jRuby 1.6.7) #13

Closed jcoyne closed 11 years ago

jcoyne commented 12 years ago

undefined method xpath' for nil:NilClass /home/hyrdadm/.rvm/gems/jruby-1.6.7/gems/rdf-rdfxml-0.3.5/lib/rdf/rdfxml/reader.rb:170:ineach_statement'

gkellogg commented 12 years ago

Unfortunately, jRuby doesn't work particularly well, largely due to issues with Nokogiri. Work on a REXML/Builder version is underway, but is down on my list a bit.

Please provide a test cases, and I'll add it to examples that I track. Eventually, I do want to get this, and other gems, working on jRuby.

phlegx commented 12 years ago

My input XML data is:

<?xml version='1.0' encoding='UTF-8'?>
<sparql xmlns='http://www.w3.org/2005/sparql-results#'>
    <head>
        <variable name='s'/>
        <variable name='p'/>
        <variable name='o'/>
    </head>
    <results>
        <result>
                ...

Whit this code I get only the first statement of the rdf xml. But I need the real data in the children nodes (result).

RDF::RDFXML::Reader.new(xml) do |reader|
  reader.each_statement do |statement|
    block.call(statement)
   end
end

Output is only one statement:

<RDF::Statement:0x2e7dc48(_:g49076660 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2005/sparql-results#sparql> .)>

How can I navigate to the results?

gkellogg commented 12 years ago

Firstly, full support for RDF/XML in jRuby may be problematic, as Nokogiri does not run the same. Also, SPARQL results aren't actually RDF/XML; there's a separate format for SPARQL results. The sparql-client gem includes a parser for both XML and JSON variations. Look at SPARQL::Client#parse_response, and in particular SPARQL::Client.parse_xml_bindings.

phlegx commented 12 years ago

Hi Gregg!

Thank you for the answer. I don't use jRuby. I use the normal Ruby. I have see the SPARQL-client gem. But how can I integrate it to my rdf-sesame gem?

gkellogg commented 12 years ago

Sorry, the jRuby bit was the original topic of the issue.

You should just be able to require "sparql/client".

In your Gemspec or Gemfile, add gem "sparql-client"

jcoyne commented 12 years ago

I'm pretty sure the original issue is due to this issue in nokogiri:

https://github.com/tenderlove/nokogiri/issues/683